Two-phase cooling system for cooling power electronic components

ABSTRACT

A two-phase cooling system for cooling power electronic components comprises a condenser section and an evaporator section, each with at least two metal sheets partially bonded together, the at least two metal sheets forming at least one first fluid channel or second fluid channel, respectively being arranged between two bonded areas of the at least two metal sheets. These channels form a continuous, sealed fluid channel, which connects the condenser and evaporator sections. A power electronic element can be arranged on a first main side of the evaporator section within a contact area, and the two-phase cooling system can be pressed against the power electronic component. A support plate is arranged on a second main side of the evaporator section, the second main side being opposite the first main side. The support plate comprises at least one projecting part, which contacts the evaporator section within the at least one bonded area or at least one support element is arranged within the at least one first fluid channel.

TECHNICAL FIELD

The invention relates to the field of power electronics and moreparticularly to a two-phase cooling system for cooling power electroniccomponents and a power electronic system according to the preamble ofthe independent claims.

BACKGROUND ART

DE 100 07 066 shows an arrangement for cooling electronic components.The arrangement comprises a two-phase cooling system with an evaporatorpart and a condenser part, in both of which channels have been formed bya roll-bonding process, the channels between both parts being connectedand being partially filled with a fluid. The electronic component isarranged on the evaporator part. When heat is produced in the evaporatorpart by the electronic component, the fluid evaporates and expends intothe condenser part. The condenser part is connected to a cooling bodywith cooling fins, which are air-cooled. For producing the roll-bondedchannel structure thin metal sheets are used. Therefore, the structureis mechanically weak, so that not much pressure can be applied to thisstructure. Therefore, only electronic components with small footprintand heat flux can be cooled.

EP 1 150 086 shows a two-phase cooling system for computers with twoflexible metal sheets, which are spot welded in the central portion inorder to form fluid channels. Both sheets are sealingly connected ontheir peripheral portions. The fluid channels are partly filled with afluid. In absence of heat the fluid channels are flat. If heat ispresent, the fluid can evaporate due to absorption of heat so that thefluid channels are expanded and form protruding facets. A support plateis connected to the heat producing element merely on the periphery ofthe cooling system for ensuring the volume-varying capability of thecooling system. DE 10 2004 007 219 shows a cooling system with a plate,which is on one side in contact with a heat producing element and on theother side with cooling fins. The plate and cooling fins havecorresponding recesses, between which one end of stiff cooling pipes isarranged. The pipes are bended in a u-form and the second end of thepipes is led through through-holes in the cooling fins in an areafurther away from the heat producing element. In case of heat, the heatis transported through the plate to the first end of the cooling pipesand by evaporation to the second end of the cooling pipes. Then the heatis led away from the cooling fins.

SUMMARY

It is an object of the invention to provide a two-phase cooling systemfor cooling power electronic components, which cooling system is capableof cooling large electronic components, which produce a high amount ofheat and to provide a power electronic system with such a two-phasecooling system.

This object is achieved by a semiconductor two-phase cooling systemaccording to claim 1 and by a power electronic system according to claim4.

The inventive two-phase cooling system comprises a condenser section andan evaporator section. The evaporator section comprises at least twometal sheets, which are partially bonded together and between two suchbonded areas a first fluid channel is formed. The condenser section alsocomprises at least two metal sheets, which are partially bonded togetherand between two such bonded areas a second fluid channel is formed.Preferably, the cooling system comprises two metal sheets, each beingformed integrally from one piece from the evaporator section to thecondenser section.

The at least one first and second fluid channel form at least onecontinuous, sealed fluid channel, by which the condenser and evaporatorsection are fluid-conductive connected. A power electronic element canbe arranged on a first main side of the evaporator section within acontact area. On the contact area of the two-phase cooling system thepower electronic component can be pressed. The cooling system has atleast one of the following features:

-   -   On a second main side of the evaporator section, which second        side is opposite the first main side, a support plate is        arranged. The support plate comprises at least one projecting        part, which contacts the evaporator section within the at least        one bonded area. Or:    -   At least one support element is arranged within the at least one        first fluid channel.

The inventive cooling system has the advantage that the system has ahigh mechanical strength from all sides even if the fluid channelstructure itself is mechanically weak. The at least one first fluidchannel and the second fluid channel are self supporting. The form ofthe fluid channels is independent of the pressure inside the fluidchannels and the channels are not deformed by the enhanced pressure incase of heat present. In case of no heat, the channels keep their shape,i.e. they do not collapse and the cross-section of the fluid channels isnot altered by the pressure in the channels due to evaporation of thefluid. The support element or support plate strengthens the coolingsystem even if the first fluid channel is large or many first channelsare used.

A good thermal contact can be achieved between the cooling system and aheat emitting component, because by the at least one projecting part ofthe support plate the cooling system can be pressed against the heatemitting component. Therefore, when the cooling system is pressed to theheat emitting component from the sides by clamps or screws as it istypically done, the cooling system cannot bend and the fluid channelscannot collapse. If the electronic component has a large surface a greatamount of heat can be transmitted to the cooling system, because thechannels within the cooling system can be made large without the dangerof getting mechanically instable channels, because even with thin wallsaround the fluid channels, i.e. with thin metal sheets and largediameters of the fluid channels, the channel structure can be mademechanically stable even if the cooling system is pressed against theelectronic component. In case of a support element being arranged withinthe at least one first fluid channel a minimum distance is achieved, sothat the fluid channels cannot collapse.

BRIEF DESCRIPTION OF DRAWINGS

The subject matter of the invention will be explained in more detail inthe following text with reference to the attached drawings, in which:

FIG. 1 shows a view on a first embodiment of the power electronic systemaccording to the invention; and

FIG. 2 shows a top view on the evaporator section on another embodimentof the power electronic system according to the invention as seen fromthe second main side.

The reference symbols used in the figures and their meaning aresummarized in the list of reference symbols. Generally, alike oralike-functioning parts are given the same reference symbols. Thedescribed embodiments are meant as examples and shall not confine theinvention.

DETAILED DESCRIPTION

In FIG. 1 a power electronic system with a two-phase cooling system 2and a power electronic component 1 according to the invention is shown.With such a cooling system 2 power electronic components 1, whichproduce a high amount of heat, can be cooled. The two-phase coolingsystem comprises a condenser section 22 and an evaporator section 21.The evaporator section 21 comprises two metal sheets 23, 23′, which arepartially bonded together. A first fluid channel 4 is formed between twobonded areas of the at least two metal sheets 23, 23′. The first fluidchannel is self supporting. The condenser section 22 also comprises twometal sheets, which are partially bonded together. A second fluidchannel is formed between two bonded areas of the at least two metalsheets. The second fluid channel is self supporting. The at least onefirst 4 and second fluid channel form at least one continuous, sealedfluid channel, which connects the evaporator section 21 and thecondenser section 22. The two-phase cooling system 2 is, therefore, athermosyphon. In the at least one sealed fluid channel a fluid isfilled. A power electronic component 1 is arranged on the first mainside 211 of the evaporator section 21 within a contact area 213. In theevaporator section 21, a second main side 212 lies opposite the firstmain side 211. A support plate 5 is arranged on this second main side212. The support plate 5 comprises at least one projecting part 51,which contacts the evaporator section 21 within the at least one bondedarea and by which at least one projecting part 51 the cooling system 2is pressed against the power electronic element 1. On the outside of thecondenser section 22 cooling fins 3 are arranged.

In a preferred embodiment thermal interface material is arranged betweenthe at least one first fluid channel 4 and the power electronic element1, thereby improving the thermal contact and thermal heat transfer.

Heat produced in the power electronic component 1 is transferred to thetwo-phase cooling system 2. Within the evaporator section 21 the heatleads to latent heat of the fluid in the first fluid channels 4, so thatthe fluid starts to boil and vapour is produced. This vapour istransmitted through the first fluid channels 4 to the second fluidchannels in the condenser section 22, the second fluid channels beingdirectly connected to the first fluid channels 4 and forming continuousfluid channels. In the condenser section 22 the vapour is condensed,thus releasing the latent heat. This effect is exaggerated by thecooling fins 3, which are either gas-cooled, typically air-cooled, orliquid-cooled, typically water-cooled. Alternatively, it is possible tocool the second cooling channels by direct liquid cooling or acoldplate, thus without fins. The condensed fluid flows back through thesame fluid channel or through another fluid channel to the evaporatorsection 21. Such a two-phase cooling system 2 does not need a pump forthe transport of the cooling fluid away from the heat producing powerelectronic component. In such a two-phase cooling system the fluid istransported either by gravity force or by capillary forces.

FIG. 2 shows a top view on the evaporator section 21 according toanother embodiment of the inventive two-phase cooling system 2 from thesecond main side 212. Three single first cooling channels 4 are shown;each having a sealed end 41, but there could also be more or less firstfluid channels 4 or the fluid channels could be interlinked, so that thefluid could get from one channel to the other. In any case, the fluidchannel arrangement is sealed, so that no fluid can get out of thesechannels. On one end 42 the first fluid channels are open and connectedto the second fluid channels (not shown in FIG. 2). Typically, theevaporator section and condenser section 21, 22 are integrally made ofone piece, i.e. of one metal sheet 23′ on the second main side 212,which is a continuous sheet in the evaporator and condenser section 21,22, and of another metal sheet 23 on the first main side 21 1, which isalso a continuous sheet in the evaporator and condenser section 21, 22.In FIG. 2 the support plate 5, which has not been mounted yet on thesecond main side 212 of the evaporator section 21 can be seen. Thesupport plate 5 has projecting parts 51, which lie on the bonded areasof the metal sheet 23′ after mounting. When the cooling system 2 iscompressed together with the power electronic component 1, the supportplate 5 only presses on the mechanically strong bonded areas of theevaporator section, thus giving a good thermal contact between the firstfluid channels 4 and the power electronic component 1 without stressingthe mechanically weak material in the fluid channel areas.

In a preferred embodiment the projecting parts are arranged outside anarea on the second main side 212, which area lies opposite the contactarea 213, which is on the first main side 211 and on which the powerelectronic component 1 is arranged. The contact area 213 is shown inFIG. 2 by a dashed line. In that case the projecting parts 51, which donot contribute appreciably to the heat transmittal are outside the mainheat path. In case that the power electronic component 1 comprises morethan one semiconductor chip the projecting parts 51 of the support plate5 can be arranged on such an area of the second main side 212, that nochip or in general, no heat generating components is arranged on thefirst main side 211 directly opposite of the area, on which theprojecting parts 51 are arranged. This area may even be within the areaopposite the contact area 213.

The at least one first fluid channel 4 can even be made as one bigcavity in the contact area 213, so that the heat from the powerelectronic component 1 can be transmitted to the fluid over a largearea. In another preferred embodiment the at least one first fluidchannel 4 covers at least most of the area on the second main side 212,which lies opposite the contact area 213. This could be advantageousbecause of construction and mechanical reasons.

If it is feasible with the manufacturing process, at least one supportelement can be integrated in the first ands/or second fluid channels(not shown in a figure), so that the two-phase cooling system can bemade in a very compact form. The support element in the form of a spaceris arranged within the fluid channel in such a way that a minimumdistance between the at least two metal sheets (23, 23′) is achieved andthe fluid channel cannot collapse. The spacer can be pins or a stickbetween the two metal sheets 23, 23′), thin foils or plates extendingtheir length along the length direction of the fluid channel, whichfoils or plates are stable enough not to be pressed together, a grid orany other spacer, which stabilizes the shape of the fluid channels.Preferably, the at least one support element is formed and arranged insuch a way that the at least one first fluid channel 4 cannot becompressed by forces, which are applied in a perpendicular direction tothe second main side 212.

The channel structure in the evaporator and/or the condenser section 21,22 can be made by a roll-bonding process. Any other method, by which twometal sheets are partially bonded, leaving a channel between two bondedareas is also possible. The bonded areas could e.g. also be achieved bygluing, soldering or brazing and applying temperature and/or pressure tothe sheets to be bonded. The form of the channels can be made before,during or after bonding. For forming the sheets before bonding, at leastone of the sheets is coldworked in the desired shape for the channels.For forming the sheets after bonding, the channel structure is inflatedafter the bonding, e.g. as it is done in roll-bonding, where air ispressed into the space between two bonded areas under high pressure.

REFERENCE LIST

1 power electronic component

2 two-phase cooling system

21 evaporator section

211 first main side

212 second main side

213 contact area

22 condenser section

23, 23′ metal sheet

3 cooling fins

4 first fluid channel

41 sealed end

42 open end

5 support plate

51 projecting part

1. Two-phase cooling system for cooling power electronic components, thecooling system comprising a condenser section and an evaporator section,the evaporator section comprising at least two metal sheets partiallybonded together, the at least two metal sheets forming at least onefirst fluid channel being arranged between two bonded areas of the atleast two metal sheets and the condenser section comprising at least twometal sheets partially bonded together, the at least two metal sheetsforming at least one second fluid channel being arranged between twobonded areas of the at least two metal sheets, the at least one firstand second fluid channel forming at least one continuous, sealed fluidchannel, which connects the condenser and evaporator sections, whereinthe evaporator section comprises a first main side with a contact areafor contacting a power electronic element, and wherein the two-phasecooling system has at least one of the following features: a supportplate is arranged on a second main side of the evaporator section, thesecond main side being opposite the first main side, the support platecomprising at least one projecting part, which contacts the evaporatorsection within the at least one bonded area or at least one supportelement is arranged within the at least one first fluid channel. 2.Cooling system according to claim 1, wherein in case of a support platebeing arranged on a second main side of the evaporator section, the atleast one projecting part of the support plate is arrangeable outside anarea on the second main side, which lies opposite of the contact area.3. Cooling system according to claim 1, wherein the two-phase coolingsystem comprises at least one spacer as support element.
 4. Powerelectronic system with a power electronic element and a cooling systemaccording to claim
 1. 5. Power electronic system according to claim 4,wherein a thermal interface material is arranged between the at leastone first fluid channel and the power electronic element.
 6. Method formanufacturing a cooling system according to claim 1, wherein the atleast one first and/or second fluid channel is made by a roll-bondingprocess.
 7. Power electronic system with a power electronic element anda cooling system according to claim
 3. 8. Method for manufacturing acooling system according to claim 3, wherein the at least one firstand/or second fluid channel is made by a roll-bonding process. 9.Two-phase cooling system for cooling power electronic components, thecooling system comprising a condenser section, the condenser sectioncomprising at least two first metal sheets partially bonded together,the at least two first metal sheets forming at least one first fluidchannel being arranged between two bonded areas of the at least twofirst metal sheets; and an evaporator section, the evaporator sectioncomprising at least two second metal sheets partially bonded together,the at least two second metal sheets forming at least one second fluidchannel being arranged between two bonded areas of the at least twosecond metal sheets, wherein the at least one first and second fluidchannels form at least one continuous, sealed fluid channel, whichconnects the condenser and evaporator sections, wherein the evaporatorsection comprises a first main side with a contact area for contacting apower electronic element, and wherein the two-phase cooling system hasat least one of a support plate, or at least one support elementassociated with the evaporator section.